Volume 18, Issue 4, Pages 563-577 (April 1997) Cajal-Retzius Cells Regulate the Radial Glia Phenotype in the Adult and Developing Cerebellum and Alter Granule Cell Migration  Eduardo Soriano, Rosa M. Alvarado-Mallart, Nicole Dumesnil, José A. Del Río, Constantino Sotelo  Neuron  Volume 18, Issue 4, Pages 563-577 (April 1997) DOI: 10.1016/S0896-6273(00)80298-6

Figure 1 Schematic Drawing and Composition of Donor Tissues for the Grafting Experiments (A) Diagram of the transplantation procedures. In some experiments (top), pieces of tissue from E15 embryos containing all the layers of the cerebral cortex were grafted into adult host cerebella. In other experiments (bottom), pieces from E15 neocortex were tangentially cut in a vibratome, and the slices containing the marginal zone layer I (MZ) were used for transplantation. VZ, ventricular zone. (B) Frontal section from the neocortex of an E15 embryo immunoreacted with calretinin antibodies illustrating the cell composition and layering of the cortex at the age at which the vibratome slices were taken. Calretinin+ CR cells (arrows) are densely packed in the marginal zone layer I (MZ). Immunoreactive neurons are very scarce in the remaining cortical layers, including the cortical plate (CP), intermediate zone (IZ), and ventricular zone (VZ). In the subventricular zone (SVZ), many immunoreactive, small cells can be seen (open arrows). (C) Tangential view of layer I at P2 in a thick neocortical slice immunoreacted for calretinin, illustrating CR cells with typical pearl-shaped to ovoid perikarya and a single thick dendrite. (D and E) Transverse cryostat sections (20 μm thick) of tangential vibratome slices through the marginal zone obtained as shown in (A), illustrating the cellular composition of the vibratome slices used for transplantation and culture experiments. The section in (D) was immunoreacted for calretinin and shows numerous CR cells (arrows). The section in (E) was stained with cresyl violet and shows that the vibratome slice contains, in addition to cell components of the marginal zone (MZ), some clusters of neurons from the upper cortical plate (open arrows) but not neurons from the deep cortical plate, the subplate, the intermediate zone, or the ventricular zone. Scale bars = 100 μm, (B) and (C); and 50 μm, (D) and (E). Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)

Figure 2 RC2 Induction in Adult Cerebella 7 Days after Transplantation of E15 Neocortex (A) Sagittal cerebellar section immunolabeled with the RC2 antibody shows the allocation of the graft (asterisks) within several cerebellar folia and the patchy induction (arrows) of RC2 immunoreactivity in the Bergmann glia of the host cerebellum. ML, molecular layer; PL, Purkinje cell layer; and GL, granule cell layer. (B) Photomicrograph from a graft immunostained with calretinin antibodies illustrating numerous CR cells inside the cortical graft grouped around a blood vessel (bv). Note the intense calretinin staining of the host parallel fibers in the molecular layer (ML). (C) RC2 immunostaining of host glial cells exhibit the typical morphology of Bergmann glia (arrows). RC2+ cell bodies are located at the granule cell layer–molecular layer (GL–ML) interface (arrows) and have several varicose processes (arrows) that ascend perpendicularly in the molecular layer. (D) Camera-lucida reconstruction illustrates the extent of RC2 immunostaining in sagittal sections of an adult host cerebellum after grafting pieces of E15 neocortex (asterisks). Note the relationship between the distribution of CR cells identified by calretinin immunocytochemistry (dots) and RC2+ Bergmann fibers. Mediolateral sections spaced 250–350 μm. Scale bars = 100 μm, (A); 50 μm, (B) and (C); and 500 μm, (D). Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)

Figure 3 Induction of RC2 Immunostaining in Adult Cerebella 7–10 Days after Transplantation of CR Cell-Enriched Slices. Abbreviations as in Figure 2 (A) Photomicrograph illustrating large palisades of intense RC2-immunoreactive Bergmann glia (arrows) at 7 DAG. (B) High magnification view of the palisade labeled by open arrow in (A). Note the dense RC2 immunolabeling of Bergmann glial cells and processes (arrows) spanning the molecular layer (ML). (C) RC2 immunostaining after transplantation of a control vibratome slice containing the ventricular and subventricular zones (enriched in radial glia and cortical progenitors) from E15 embryos (7 DAG). Some clusters of RC2+ cells (arrows) occur inside the cortical graft (asterisks). However, no RC2 immunostaining is observed in the host cerebellum (to the left). (D) Section from a cerebellum grafted with a CR cell–enriched slice taken from an NSE–lacZ transgenic embryo (7 DAG). The section has been developed with Xgal and then immunoreacted with RC2 antibodies. Xgal-positive CR cells (open arrows) appear located at the cerebellar fissure, just above the sites of Bergmann glia RC2 reexpression (arrows). (E) RC2-immunoreacted section shows RC2+ cells (arrows) in the molecular layer (ML), with bipolar morphology distinct to that of Bergmann fibers. Such bipolar RC2-immunoreactive cells were observed only occasionally. (F) Camera lucida reconstruction illustrates the extent of RC2 reexpression in representative sagittal sections (spaced 250–350 μm) from an adult cerebellum grafted with a CR cell–enriched slice from an NSE–lacZ embryo. Note the correlation between the distribution of CR cells (dots), identified after Xgal staining, and clusters of RC2+ Bergmann glia. Scale bars = 100 μm, (A) and (C); 50 μm, (B) and (E); 25 μm, (D); and 500 μm, (F). Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)

Figure 4 Induction of RC2 Immunostaining in Host Bergmann Glia after Transplantation of CR Cell–Enriched Slices in Krox20–lacZ14 Transgenic Mice (7 DAG). Abbreviations as in Figure 2 (A) Fluorescence microphotograph shows the distribution of βgal-immunoreactive elements in the adult cerebellum of a Krox20–lacZ14 transgenic mouse. βgal immunolabeling occurs exclusively in Bergmann glial cells and fibers (arrows). (B and C) Pair of fluorescence photomicrographs of a section double immunolabeled with RC2 (C) and βgal (B) antibodies, after transplantation of a CR cell–enriched slice (7 DAG) in an adult Krox20–lacZ14 cerebellum. Glial fibers exhibiting RC2 immunostaining (arrows in [C]) are also βgal immunoreactive (arrows in [B]), demonstrating that RC2 induction occurs in host Bergmann glia. Scale bars = 100 μm, (A); 50 μm, (B) and (C). Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)

Figure 5 Induction of RC2 Immunolabeling in Postnatal Cerebellar Slices Cocultured with CR cells. Abbreviations as in Figure 2 (A) Schematic representation of the different coculture approaches used. Cerebellar postnatal slices were cocultured with CR cell–enriched explants (MZ) and ventricular zone–enriched explants (VZ) positioned at opposite sites at the surface of the cerebellar slices (contact confrontation assay) or above a semipermeable membrane, which was held onto the cerebellar (CB) slice (diffusible test assay). (B–E) These micrographs illustrate results obtained with the diffusible test assay using CR cell–enriched slices ([B–D], wild type; [E], homozygous reeler). (B) Dramatic induction of RC2 immunostaining in many cerebellar glial cells throughout the cerebellar slice. Most RC2+ glial cells are bipolar and appear to be randomly oriented. (C and D) High power photomicrographs illustrate examples of RC2+ cells in cerebellar slices. While some RC2+ cells (D) located in the Purkinje cell layer exhibit a radial orientation and varicose processes (arrows) that may correspond to that of immature Bergmann glia, other cells show very immature bipolar shapes (arrows in [C]) with two thick processes arising from opposite sides of the cell bodies. (E) Induction of RC2 immunostaining in a cerebellar slice cocultured with a CR cell–enriched slide from a reeler mouse embryo. Note numerous RC2+ glial cells displaying bipolar shapes (arrows) and some fasciculation of the processes. Scale bars = 100 μm, (B) and (E); and 25 μm, (C) and (D). Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)

Figure 6 Effects of CR Cells on Bergmann Glia and on Migration of Granule Cells in Cerebellar Organotypic Cultures. Arrowheads Label the Neocortical–Cerebellar Interfaces (A) Low power photomicrograph of a cerebellar slice (CB) from a Krox20–lacZ14 transgenic mouse cocultured with a CR cell–enriched slice (CR) and with a ventricular zone–containing slice (VZ) located at opposite sides. The triple coculture (8 DIV) was stained with Xgal to identify Bergmann glial cells and then immunoreacted for calbindin. Whereas blue Xgal+ Bergmann glia have penetrated and fill the CR cell–enriched explant (top), very few Bergmann glial cells penetrated and for shorter distances the VZ-enriched slice (bottom). (B) High magnification of a Krox20–lacZ14 cerebellar slice (CB, left) cocultured with a CR cell–enriched explant (CR, right) demonstrating massive ingrowth of βgal-expressing Bergmann glia in the neocortical explant (8 DIV). In the area of the neocortical slice closest to the cerebellum, Xgal+ processes show radial orientation (arrows), whereas in deep areas, Xgal-staining appears more diffuse. (C) CR cell-enriched slice (CR) cocultured with a Krox20–lacZ14 cerebellum (CB) stained with Xgal and immunolabeled with anti-calretinin antibodies to identify CR cells (8 DIV). Blue Xgal+ Bergmann glial cell processes are in close apposition with CR cells (arrows). (D) Low power view of a cerebellar slice (CB) from a β2nZ3′1 transgenic mouse cocultured with a CR cell–enriched slice (CR) and with a ventricular zone–enriched slice (VZ). The culture was stained with Xgal to visualize cerebellar granule cells and then immunolabeled with an anti-calbindin antibody (10 DIV). Many blue βgal+ granule cells have migrated deep in the CR cell–enriched slice (top) where they concentrate in a band (arrows) at 400–500 μm from the cerebellar slice. Few Xgal+ granule cells have migrated into the VZ-containing slice (bottom). Boxed area is shown at higher magnification in (E). (E) High magnification of the triple coculture in (D) shows massive penetration of blue Xgal+ granule cells in the CR cell–enriched slice. (F) High power view of a β2nZ3′1 cerebellar (CB) slice cocultured with a ventricular zone–enriched slice (VZ) (10 DIV). Note the moderate migration of Xgal+ cerebellar neurons into the VZ-enriched slice. (G and H) Pair of bright-field (G) and fluorescence (H) photomicrographs of the same field in a CR cell–enriched slice (CR) cultured with a β2nZ3′1 cerebellar slice (CB), showing migration of Xgal+ cerebellar granule cells in the CR cell–enriched explant (G) and survival of many CR cells identified by calretinin immunofluorescence (H) (8 DIV). Arrows labeling to same reference fields. (I) Double-exposed photomicrograph (bright field and epifluorescence microscopy) of a CR cell–enriched slice (CR) cultured with a β2nZ3′1 cerebellar slice (CB) illustrating the close spatial relationships between the distribution of CR cells (arrows) identified with calretinin antibodies (yellow) and the clusters of blue Xgal+ granule cells (8 DIV). Scale bars = 250 μm, (A) and (D); 100 μm, (B), (E), and (F); and 50 μm (C), (G), (H), and (I). Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)

Figure 7 Summary Scheme on the Main Findings of the Present Study (A) While transplantation of CR cells in the adult cerebellum leads to induction of RC2 immunoreactivity (bold) only in Bergmann glia (top), CR cells induce a RC2+ radial glia phenotype in Bergmann glia and in other astrocytes in the postnatal cerebellum (bottom). Moreover, postnatal cerebellar glial cells shift to an immature bipolar morphology typical of immature radial glia. (B) CR cells in contact with the proliferative external granule cell layer (EGL) of postnatal cerebellar slices (left) lead to a massive ingrowth of Bergmann glial cell processes and cells into the CR cell–enriched explant (right). At the same time, postmitotic granule cells, which normally migrate toward the internal granule cell layer (IGL), now migrate also in the opposite direction, deep into the CR cell–enriched slice. Neuron 1997 18, 563-577DOI: (10.1016/S0896-6273(00)80298-6)